Kubernetes Node Disk Pressure Threshold Adjustment (evictionHard)

When node disk usage exceeds a certain threshold, the Disk Pressure condition is triggered and pods are evicted.
Default hard thresholds (Linux-based):

• memory.available < 100Mi
• nodefs.available < 10%
• imagefs.available < 15%
• nodefs.inodesFree < 5%

In other words, by default, DiskPressure occurs when root (nodefs) reaches 90% usage and imagefs reaches 85% usage.

Adjustment

evictionHard:
  imagefs.available: 5%
  memory.available: 100Mi
  nodefs.available: 5%
  nodefs.inodesFree: 5%

• Adjusted: All disk-related thresholds (nodefs.available, imagefs.available, nodefs.inodesFree).
• Unchanged: memory.available remains at the default 100Mi.

Result (usage basis):

• nodefs.available: 10% free → 5% free → threshold shifted from 90% usage to 95% usage
• imagefs.available: 15% free → 5% free → threshold shifted from 85% usage to 95% usage
• nodefs.inodesFree: remains the same (5%)
• memory.available: remains the same (100Mi)

Threshold Key Descriptions

• nodefs.available: Free space threshold of the root filesystem
• imagefs.available: Free space threshold of the container image filesystem
• nodefs.inodesFree: Free inode ratio threshold
• memory.available: Free memory threshold on the node

📌 Summary: Disk usage can now reach up to 95% before DiskPressure is triggered.
→ Greatly reduces the free-space safety buffer compared to the defaults.
⚠️ Risk: Increases the chance of logging failures, updates failing, or temporary file write errors when disks fill up.

Modify kubelet Config

1. Locate kubelet config file

ps -ef | grep kubelet

Check the path after the --config option (e.g., /etc/kubernetes/kubelet-config.yaml).

2. Edit the file

vi /etc/kubernetes/kubelet-config.yaml

Add or update the following block:

evictionHard:
  imagefs.available: "5%"
  memory.available: "100Mi"
  nodefs.available: "5%"
  nodefs.inodesFree: "5%"

Restart kubelet

systemctl restart kubelet

Verify

kubectl describe node <node-name> | grep -A5 Conditions

Conclusion

• Default: DiskPressure at 90% nodefs usage / 85% imagefs usage
• After adjustment: DiskPressure delayed until 95% usage for both nodefs and imagefs
• Apply by modifying kubelet config and restarting kubelet

🛠 마지막 수정일: 2025.09.18